She sees a strange Bunny (Vanny)

Her costume gives her confidence as she explores the Pizzaplex after dark. She is walking through the empty atrium when she sees an odd sight. There's someone else her in a costume she's never seen. It's a rabbit costume but not based on Bonnie or any other Fazbear character. The costume is of a white rabbit with a large blue bowtie and red eyes. Cassie can tell from how the rabbit skips it must be another person. For a second she wonders if Gregory was hiding he was a furry but Cassie realizes it's a female rabbit.

The bunny stops moving and turns to look right at Cassie making her flinch. The situation is a bit off putting but seeing someone else in a tight costume like hers makes Cassie curious who it is.